1. Field of the Invention
The invention relates to a measurement device, especially for process measurement engineering, with a housing, with a sensor element and with an adjustment element, especially a potentiometer, for setting at least one parameter of the measurement device.
2. Description of Related Art
There are many applications for measurement devices for process measurement engineering. Thus, for example, the pressure, the temperature, the fill level, the flow velocity or the flow amount of gases, of liquid or solid media, but also of bulk material are monitored or measured. In doing so, there are a plurality of different measurement principles for determining the individual parameters. Thus, for example, the fill level of a liquid can be determined by means of ultrasound, radar or guided microwaves. In pressure sensors which are used for monitoring and measuring the system pressure in hydraulic and pneumatic applications, there are, for example, those with a capacitive measurement principle. These pressure sensors, as the sensor element, have a capacitive cylindrical pressure measurement cell which formed of a base body and a membrane which are held at a specific distance from one another and are joined hermetically tight to one another by a joining material, for example, brazing solder. Besides these pressure sensors which have a capacitive measurement principle, there are also pressure sensors which have a strain gauge (DMS) or DMS resistors as the sensor element. In these pressure sensors, the DMS resistors are applied to the side of the membrane facing away from the medium, the resistance value of the DMS resistors depending on the sagging of the membrane, and thus, likewise being a measure of the pressure on the membrane.
The individual measurement methods have different advantages and disadvantages specific to the application. In order to meet the partially very different needs of the individual users, therefore a very great diversity of types of measurement devices is necessary; due to small numbers and high warehousing costs, this leads to a high final cost for the measurement devices. The diversity of types is further increased in that, on the one hand, there are so-called compact devices in which the measurement unit and the evaluation device are jointly accommodated in a housing, and on the other hand there, are those measurement devices in which the evaluation device is spatially separate from the measurement unit and is connected to it via a connecting cable.
It is common to both types of measurement devices that it is frequently necessary or at least desirable to be able to set at least one parameter of the measurement device as much as possible on site. The parameter which is to be set can be, for example, the operating point. Likewise, by inputting two operating points, the measurement range of the measurement device can be adjustable. In addition to one or more adjustable operating points, it can also often be necessary to adjust a value for the hysteresis. In addition to the operating point or limits of the measurement range, the parameters which are to be set can also include the choice of a certain medium, a temperature range or a time delay.
In simple and thus relatively economical measurement devices, the parameter is generally set via a potentiometer which is located in the housing and which has a setscrew which is accessible from the outside. The setscrew can be actuated with a normal slotted or Phillips head screwdriver. These potentiometers are available in a variety of versions so that setting the parameter of the measurement device using the corresponding potentiometer can be very simple and economical. However, the disadvantage in using a potentiometer for setting a parameter is that accurate and reproducible setting of the parameter is not possible solely with a potentiometer.
For this reason, in the meantime, there are a host of measurement devices in which the measurement unit and the evaluation device are accommodated jointly in a housing, the evaluation unit having especially an indication and setting display. With these displays on, the one hand, accurate and reproducible setting of a parameter via the corresponding keys is possible, and on the other hand, in addition to the actual measurement values, the adjusted parameter can also be indicated using a display. However, these displays, which often have a LCD display or a bar graph, are relatively expensive, and moreover, require additional room which is only very conditionally available in so-called compact devices. In addition, these displays have the disadvantage that they increase the power consumption of the measurement devices overall; this is especially disadvantageous in 2-lead devices.
Published German Patent Application Nos. DE 41 20 752 and DE 196 16 658 disclose a cylindrical pressure measurement device with a lower part which is provided with a receiver, with an upper part and with an indication and adjustment display. These pressure measurement devices are, for example, screwed into pressure vessels or into gas- or liquid-carrying pipelines, forming a seal. When such a measurement device is screwed into a wall, the resulting angular position then depends on the torque with which the measurement device lower part is screwed into the wall. The resulting angular position can be unfavorable since in this angular position the electric leads, the display or control keys are only accessible with great difficulty or not accessible at all. To align the measurement device upper part such that the electric leads, the display or control keys are easily accessible, the measurement device upper part can be turned relative to the measurement device lower part around the lengthwise axis of the measurement device lower part. In this way, good readability of the display and good accessibility of the control keys are possible, but special measures are necessary to achieve adequate axial fixation. In addition, there are the problems of the space required by the display and the additional power consumption.